Roofing underlayment is a critical layer that protects a home from water intrusion and weather damage. This article compares roofing felt and ice and water shield, explaining their materials, performance, cost, installation, code considerations, and best use cases to help homeowners and contractors choose the right underlayment for U.S. climates and roof types.
| Feature | Roofing Felt | Ice And Water Shield |
|---|---|---|
| Material | Asphalt-saturated paper or synthetic fabric | Self-adhered rubberized asphalt membrane |
| Primary Function | Temporary weather barrier and secondary protection | Waterproofing at roof edges, penetrations, and vulnerable areas |
| Water Resistance | Water resistant, not fully waterproof | Waterproof and self-sealing |
| Installation Difficulty | Relatively easy; roll and fasten | More demanding; adhesive bonding and surface prep |
| Cost | Lower cost per square | Higher cost per square; often used selectively |
| Lifespan | 10–30 years depending on type | 20–50 years when installed correctly |
What Is Roofing Felt?
Roofing felt, often called tar paper, is an underlayment made from cellulose or fiberglass fabric saturated with asphalt. Traditional felt is available in 15-pound and 30-pound weights, and synthetic felts are made from polypropylene or polyester with enhanced tear resistance and moisture performance.
What Is Ice And Water Shield?
Ice and water shield is a self-adhering, rubberized asphalt membrane typically sold in rolls with a polyethylene film backing. It creates a continuous waterproof barrier that seals around nails and conforms to roof contours, making it ideal for eaves, valleys, chimneys, and skylights.
Material Composition And Performance
Roofing felt’s asphalt saturation provides a basic moisture barrier and temporary protection during installation. Synthetic options resist tearing, stretch less, and shed water better than organic felt.
Ice and water shield combines asphalt with a rubber polymer adhesive that bonds to the roof deck. Its adhesive properties allow it to seal penetrations and prevent concealed leaks, especially useful in freeze-thaw regions where ice dams form.
Where Each Product Excels
Roofing felt excels as a broad-area underlayment beneath shingles to protect against wind-driven rain and provide a smooth substrate. It is a cost-effective choice for standard roof installations where full waterproofing beneath the entire roof surface is not required.
Ice and water shield excels at localized waterproofing. It is most effective at roof edges, eaves, valleys, around chimneys, and under step flashing, where water backup or concentrated leakage risk is high.
Building Codes And Manufacturer Requirements
Many building codes require ice and water shield in specific locations, especially in cold-climate zones prone to ice dams. Local codes vary, so consulting the municipal code is essential.
Shingle manufacturers often specify underlayment types to maintain shingle warranties. Failure to follow manufacturer underlayment recommendations can void the roof warranty, so review product instructions before installation.
Installation: Steps, Tools, And Best Practices
Roofing Felt Installation
Felt is rolled out horizontally from the eave upward, overlapped per manufacturer specs, and fastened with roofing nails or staples. Proper overlap and fastener placement are critical to prevent wind uplift and water infiltration.
Ice And Water Shield Installation
Ice and water shield requires careful substrate preparation: the deck must be clean, dry, and free of frost. The liner is peeled back and the membrane pressed firmly to the deck, smoothing wrinkles and ensuring full adhesion.
Installation temperature limits and adhesion testing are important. Cold or wet surfaces can compromise adhesion and performance, so installing during suitable weather or following cold-weather techniques is necessary.
Cost Comparison And Budgeting
Roofing felt is significantly less expensive per square than ice and water shield. For a typical roof, felt may cost a fraction of the material cost of applying ice and water shield over the entire deck.
Because ice and water shield is pricier, many contractors use a hybrid approach: apply ice and water shield at eaves, valleys, hips, and penetrations and use felt elsewhere. This balances budget and performance.
Longevity And Durability
Organic felt brittle over time and can tear during high winds or prolonged UV exposure. Synthetic felts resist tearing and can have longer service lives.
Ice and water shield generally offers superior durability where used correctly. Its adhesive nature and waterproofing properties help prevent hidden leaks and deck rot. Lifespan depends on proper installation and compatibility with roof covering materials.
Climate Considerations
In cold climates with freeze-thaw cycles and heavy snowfall, ice and water shield at eaves and valleys is a common requirement to protect against ice dams.
In warm, humid climates, moisture management and ventilation are critical. Synthetic felts that reduce moisture trapping may be preferable, while overuse of waterproof membranes without proper flashing can trap moisture and cause issues.
Compatibility With Roof Coverings
Both products are compatible with asphalt shingles, metal roofing, tile, and slate when installed per manufacturer guidelines. However, the adhesive of ice and water shield can complicate removal during roof replacement.
When installing tile or slate, installers must ensure membranes do not interfere with mechanical fastening or create unanticipated moisture retention. Follow specific system installation details for each roof covering.
When To Use Both: Hybrid Strategies
A best-practice approach for many U.S. roofs is a hybrid underlayment strategy: use ice and water shield in vulnerable areas and roofing felt over the rest of the deck. This provides targeted waterproofing while controlling costs.
Specific recommended locations for ice and water shield include eaves (36 inches or per code), valleys, around skylights, chimneys, roof-to-wall intersections, and low-slope roof sections.
Common Mistakes And How To Avoid Them
- Installing ice and water shield over wet or frosty decks reduces adhesion; ensure dry surfaces.
- Overlapping ice and water shield incorrectly can create channels for water; follow manufacturer overlap specs.
- Using only felt in ice-dam-prone areas can lead to concealed leaks; add waterproof membranes where required.
- Failing to coordinate underlayment with flashing details will compromise performance; integrate flashing, underlayment, and shingles.
Cost-Benefit Analysis For Homeowners
Homeowners should weigh upfront material and labor costs against potential long-term savings from reduced leak risk and avoided roof deck repairs. Spending more on targeted waterproofing often prevents costly interior damage.
Insurance considerations may also favor enhanced underlayment in certain regions; some insurers provide incentives for mitigation measures that lower claim risk.
Maintenance, Inspection, And Replacement
Underlayment is usually hidden, so regular roof inspections of shingles, flashings, and attic conditions help detect underlayment failures indirectly. Look for signs of moisture staining, mold, or rot in the attic.
When replacing roof coverings, inspect and, if necessary, replace underlayment. Ice and water shield may be left in place only if it’s compatible and undamaged.
Frequently Asked Questions
Is Ice And Water Shield Necessary On Every Roof?
Not always. Code and climate may dictate requirements; targeted use at vulnerable areas is common, while full-deck coverage is typically reserved for specific low-slope or high-risk scenarios.
Can Synthetic Felt Replace Ice And Water Shield?
Synthetic felt improves tear resistance and water shedding, but it is not fully waterproof like ice and water shield and will not self-seal around fasteners.
Does Ice And Water Shield Prevent Ice Dams?
Ice and water shield helps prevent leaks from ice dams by waterproofing vulnerable areas, but addressing attic insulation, ventilation, and roof surface temperature is essential to reduce ice dam formation.
Decision Checklist For Choosing Underlayment
- Review local building codes and shingle manufacturer requirements.
- Assess climate risks: ice dams, heavy rain, wind-driven rain.
- Identify vulnerable roof areas: eaves, valleys, penetrations, low slopes.
- Balance budget with risk tolerance—use hybrid approach where appropriate.
- Hire experienced installers familiar with membrane handling and roof detail integration.
Resources And Further Reading
For detailed product specifications and installation instructions, consult manufacturer technical bulletins for specific ice and water shield brands and synthetic felts. Local building departments and certified roof inspectors provide guidance tailored to regional code and climate.
Additional reputable sources include the Asphalt Roofing Manufacturers Association (ARMA) and the National Roofing Contractors Association (NRCA) for standards and best practices.
Choosing between roofing felt and ice and water shield requires evaluating climate, roof design, code, and budget; a hybrid approach often provides optimal protection and value.